Graphite intercalation compound and production method thereof

ABSTRACT

An onion-like graphite 2 is produced by irradiating an electron beam to an amorphous carbon 3 under an active aluminum nanoparticle 1. By further irradiating the electron beam to the onion-like graphite 2 to intercalate aluminum atoms constituting the aluminum nanoparticle 1 in a space between (001) plane and (002) plane of the onion-like graphite 2 having a layer structure, an intercalation compound 4 is produced. Or, after the aluminum nanoparticles were driven and disposed on the onion-like graphite by electron beam, or the like, by irradiating the electron beam to intercalate aluminum atoms in the space between the (001) plane and the (002) plane of the onion-like graphite having a layer structure, the intercalation compound is produced.

This is a division of application Ser. No. 08/626,457, filed Apr. 2,1996 U.S. Pat. No. 5,762,898.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a graphite intercalation compound and aproduction method thereof.

2. Description of the Related Art

The graphite intercalation compound is produced by intercalated adifferent kind of substance in a space of graphite or the like having alayer structure, is capable of improving electric conductivity and isapplicable to functional material such as a catalyst utilizingproperties of the intercalated substance. Various intercalationcompounds are synthesized and their physical properties and/orapplications thereof are studied.

As examples of a different kind of substance intercalated in a space ofgraphite having a layer structure, alkali metals such as Li, Na, or K,alkaline-earth metals such as Ca, Sr, or Ba, rare earth elements such asSm, Eu, or Yb, transition metals such as Mn, Fe, Ni, Co, Zn, or Mo,halogens such as Br₂, ICl, or IBr, acids such as HNO₃, H₂ SO₄, HF, orHBF₄, and compounds such as MgCl₂, FeCl₂, FeCl₃, NiCl₂, AlCl₃, or SbCl₅are reported.

Conventionally, the graphite intercalation compound intercalated adifferent kind of substance in a space having a layer structure isproduced by (a) a method of contacting graphite with a gaseous phase ora liquid phase of substance to intercalate, or (b) an electrolysis ofelectrolyte including intercalated substance using a graphite electrode.For example, a graphite intercalation compound using alkali metals isobtained by coexisting graphite with the alkali metals under a vacuumand heating them. A graphite intercalation compound using halogens isproduced by contacting graphite with a liquid phase or vapor of Br₂,ICl, or IBr. A graphite intercalation compound using alkaline-earthmetals such as Ca, Sr, or Ba, or rare earth elements such as Sm, Eu, orYb is produced by mixing graphite ultrafine powder with metal powder,applying pressure to 1 to 2 MPa, and pressureless sintered.

A graphite intercalation compound using transition metals such as Fe,Co, or Mo is produced by synthesizing an intercalation compound using achloride of these metals, and reducing the compound slowly at/or belowroom temperature using NaBH₄, LiAlH₄, Na or the like. The reductionmethod has, however, low reproducibility and a drawback that a graphiteintercalation compound of transition metals cannot be stably obtained.

Above-mentioned conventional methods for producing a graphiteintercalation compound utilizes powder calcination,powder-gaseous/liquid phase reaction, electrolysis or the like. Thesenormal production methods are suitable for obtaining a graphiteintercalation compound as an aggregate. However, a graphiteintercalation compound in a controlled shape, distribution and/orstates, for example, producing an intercalation compound on a specifiednanoscase area of graphite, cannot be produced.

As described above, conventional graphite intercalation compound hasdrawbacks of low reproducibility in intercalating transition metals in aspace of graphite having a layer structure, and of limited number ofapplicable transition metals.

Conventional methods for producing a graphite intercalation compound aresuitable for obtaining a graphite intercalation compound as anaggregate. However, a graphite intercalation compound cannot be producedin a controlled shape, distribution and/or states. To enlarge a range ofgraphite intercalation compound applications, it is needed that agraphite intercalation compound can be produced in a controlled status,i.e. selectively producing an intercalation compound on a specifiednanoscase area of graphite.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a graphiteintercalation compound and a production method thereof to enhancecontrollability such as enabling a production of an intercalationcompound on a specified nanoscale area of the graphite, andsimultaneously to improve reproducibility.

In the graphite intercalation compound of the present invention,aluminum atoms are intercalated by irradiating an electron beam in aspace between (001) plane and (002) plane of the graphite having a layerstructure.

According to the production method of the graphite intercalationcompound of the present invention, an onion-like graphite upon whichactive aluminum nanoparticles are disposed is irradiated the electronbeam under a vacuum atmosphere together with said aluminum nanoparticlesto shrink said onion-like graphite, and aluminum atoms constituting saidaluminum nanoparticles are intercalated in the space between the (001)plane and the (002) plane of said onion-like graphite having a layerstructure.

In the intercalation compound of the present invention, the aluminumatoms are intercalated in the space between the (001) plane and the(002) plane of the graphite having a layer structure. Giant fullerensthat an intercalation distance is equal to the graphite such as theonion-like graphite are cited as an example of said graphite. Thegraphite intercalation compound of the present invention is formed byirradiating the electron beam to the onion-like graphite upon which theactive aluminum nanoparticles are disposed, and by intercalatingaluminum atoms in the space between the (001) plane and the (002) planeof the onion-like graphite having a layer structure.

When disposing the active aluminum nanoparticles on the onion-likegraphite, and irradiating the electron beam on the onion-like graphite,the onion-like graphite shrank and the aluminum nanoparticles becomesmaller. Simultaneously aluminum atoms constituting the aluminumnanoparticles are intercalated in the space of the graphite having alayer structure. The electron beam having an intensity of not less than1×10¹⁹ e/cm².sec (2A/cm²) is preferred. If the intensity of the electronbeam is less than 1×10¹⁹ e/cm².sec, carbon atoms can not be activated soas to shrink the onion-like graphite. In other words, the electron beamhaving the intensity of not less than 1×10¹⁹ e/cm².sec induces alocalized heating effect and an atom displacement (knock-on) effect tothe onion-like graphite. Thereby, the onion-like graphite can shrink,and the aluminum atoms can be intercalated into the space of theonion-like graphite. The irradiation of the electron beam under a vacuumof 10⁻⁵ Pa or less is preferable. If the vacuum exceeds 10⁻⁵ Pa,remaining gas atoms may be adsorbed to prevent the aluminum atoms fromintercalating into the onion-like graphite.

As the onion-like graphite that drives and disposes the aluminumnanoparticles thereon, independent and controllable one is used. Anoriginal onion-like graphite may be in size capable of driving anddisposing the aluminum nanoparticle. For example, the originalonion-like graphite having a diameter of 10 to 30 nm is preferable.

As the active aluminum nanoparticles disposed on the onion-likegraphite, pure aluminum nanoparticles having no surface oxide film orthe like are cited as an example. A diameter of the aluminumnanoparticles is preferable in the range from 5 to 20 nm. If thediameter of the aluminum nanoparticles is less than 5 nm or exceeds 20nm, in any case, the aluminum atoms may not be intercalated correctly inthe space of the onion-like graphite having a layer structure, and maynot also be driven and disposed adequately on the onion-like graphite,as described later. Above-mentioned production method of the aluminumnanoparticles is not limited thereto. For example, the aluminumnanoparticles can be produced by irradiating the electron beam under avacuum to metastable aluminum oxide particles, as described later.

The onion-like graphite is independent and controllable which is onestarting material of the graphite intercalation compound of the presentinvention. Therefore, preferable methods for producing the onion-likegraphite are as follows:

1. Amorphous carbon such as i-carbon upon which active aluminumnanoparticles are disposed is irradiated the electron beam under avacuum atmosphere to produce the onion-like graphite.

2. Metastable aluminum oxide particles disposed upon amorphous carbonsuch as i-carbon are irradiated the electron beam under a vacuumatmosphere to produce the onion-like graphite.

In the method 1. for producing the onion-like graphite, a diameter ofthe active aluminum nanoparticles disposed on the amorphous carbon ispreferable in the range from 5 to 100 nm. If the diameter of thealuminum nanoparticles exceeds 100 nm, the amorphous carbon thereundercan not be activated sufficiently. Aluminum nanoparticles having adiameter of less than 5-nm are difficult to produce. More preferablediameter of the aluminum nanoparticles is in the range from 5 to 20 nm.

When the electron beam is irradiated to the amorphous carbon togetherwith the active aluminum nanoparticles under the above-mentionedconditions, an atomic arrangement of the amorphous carbon existed underthe active aluminum nanoparticles is changed to produce the onion-likegraphite under and around the active aluminum nanoparticles. Theonion-like graphite is obtained independently to enable irradiatingcontinuously the electron beam easily. Therefore, the onion-likegraphite is suitable for the material of the graphite intercalationcompound of the present invention.

In producing the onion-like graphite, the electron beam having anintensity of not less than 1×10¹⁹ e/cm² ·sec (2A/cm²) is preferred. Ifthe intensity of the electron beam is less than 1×10¹⁹ e/cm² ·sec, thecarbon atoms can not be activated so as to produce the onion-likegraphite. In other words, the electron beam having the intensity of notless than 1×10¹⁹ e/cm² ·sec induces a localized heating effect and anatom displacement (knock-on) effect to the onion-like graphite. Thereby,the onion-like graphite can shrink. The irradiation of the electron beamunder a vacuum of 10⁻⁵ Pa or less is preferable. If the vacuum exceeds10⁻⁵ Pa, remaining gas atoms may be adsorbed into the carbon to preventthe producing of the onion-like graphite.

The onion-like graphite produced according to the method 1. involves thealuminum nanoparticles. The aluminum nanoparticles are used as anotherstarting material of the graphite intercalation compound of the presentinvention. In other words, when the electron beam is irradiatedcontinuously to the onion-like graphite produced under the aluminumnanoparticles, the graphite intercalation compound of the presentinvention can be produced. Requirements thereof are already describedabove.

In the method 2. for producing the onion-like graphite, as themetastable aluminum oxide particles, θ-Al₂ O₃ particles which aremetastable phase of Al₂ O₃ are cited as an example. In irradiating tosuch metastable aluminum oxide particles, the electron beam having anintensity of not less than 1×10¹⁹ e/cm² ·sec (2A/cm²) is preferred. Forexample, when the electron beam having an intensity of not less than1×10¹⁹ e/cm² ·sec is irradiated to the θ-Al₂ O₃ particles disposed onthe amorphous carbon, carbon atoms are provided as constitutional atomsfrom carbon source of adsorbed atoms or impurities existed on the θ-Al₂O₃ particles to produce the onion-like graphite around the metastablealuminum oxide particles. The onion-like graphite is obtainedindependently to enable irradiating continuously the electron beameasily. Therefore, the onion-like graphite is suitable for the materialof the graphite intercalation compound of the present invention.

When using the onion-like graphite produced according to the method 2.,the active aluminum nanoparticles are driven and disposed thereon andthe electron beam is then irradiated under above-mentioned conditions toproduce the graphite intercalation compound of the present invention. Todrive and dispose the aluminum nanoparticles on the onion-like graphite,the electron beam is irradiated to the aluminum nanoparticles and isscanned to move the aluminum nanoparticles. The aluminum nanoparticlesdriven and disposed on the onion-like graphite can be driven by theelectron beam, and is in size capable of disposing on the onion-likegraphite. A diameter of about 5 to 20 nm of the aluminum nanoparticlesis preferable, as mentioned above. The aluminum nanoparticles can besecondarily produced in the production process of the onion-likegraphite by irradiating the electron beam to the θ-Al₂ O₃ particles.

The graphite intercalation compound of the present invention can beobtained by irradiating the electron beam to independently controllablegiant fullerens such as the onion-like graphite upon which the aluminumnanoparticles are disposed. Therefore, controllability of states, shapeand/or distribution that, for example, the graphite intercalationcompound can be produced on a specified nanoscale area of the graphite,and reproducibility of the graphite intercalation compound areremarkably enhanced. Moreover, the intercalation compound can beproduced in an independent state under controlled conditions. Thereby,physical properties of the intercalation compound can be grasped, andvarious operations and controls can be realized. Generally, irradiatingthe electron beam under controlled heating conditions is difficult.Therefore, it is significant that the intercalation compound can beproduced by irradiating the electron beam in a room temperature stage.

BRIEF DESCRIPTION OF THE DRAWINGS

In aid that the invention may be illustrated, more easily appreciatedand readily carried into effect by those skilled in this art,embodiments of the invention will now be described by way ofnon-limiting example any with reference to the accompanying drawings andwherein:

FIG. 1A and FIG. 1B are schematic diagrams of a method for producing agraphite intercalation compound according to the embodiment 1 of thepresent invention;

FIG. 2 is a graph showing a change of longer and shorter diameter ofaluminum nanoparticles and an onion-like graphite with the elapsed timeof the irradiation of the electron beam in the production method of thegraphite intercalation compound according to the embodiment 1 of thepresent invention;

FIG. 3 is a graph showing a change of a lattice spacing d of eachportion of the onion-like graphite with the elapsed time of theirradiation of the electron beam in the production method of thegraphite intercalation compound according to the embodiment 1 of thepresent invention;

FIG. 4 is a schematic diagram showing a production states of thealuminum nanoparticles and the onion-like graphite used for producingthe graphite intercalation compound according to the embodiment 2 of thepresent invention; and

FIG. 5A and FIG. 5B are schematic diagrams of a method for producing agraphite intercalation compound according to the embodiment 2 of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described with reference tothese drawings.

Embodiment 1

Production of active aluminum nanoparticles will be described. First,spherical θ-Al₂ O₃ particles (purity 99.8%) having a diameter of about100 nm were prepared. The particles were dispersed in alcohol, appliedto an amorphous carbon support film made of i-carbon and dried.Secondly, the amorphous carbon support film disposed spherical θAl₂ O₃particles were arranged in a room temperature stage which was disposedin a vacuum chamber of 200 kV TEM (JEOL, JEM-2010). Thirdly, the vacuumchamber was evacuated to 1×10⁻⁵ Pa. Fourthly, an electron beam having anintensity of 1.3×10²⁰ e/cm² ·sec (20A/cm²) was irradiated to the θ-Al₂O₃ particles having a diameter of about 100 nm disposed on the amorphouscarbon support film. With the irradiation of the electron beam, thealuminum nanoparticles having a diameter of about 5 to 15 nm wereproduced on the amorphous carbon support film.

Using the aluminum nanoparticles, an onion-like graphite and a graphiteintercalation compound thereof were produced. With leaving the TEMvacuum (constant vacuum level) where the amorphous carbon support filmwas disposed, aluminum nanoparticles having a longer diameter of about15 nm were selected from the aluminum nanoparticles on the carbonsupport film, the electron beam having an intensity of 1.3×10²⁰ e/cm²·sec (20A/cm²) was irradiated (irradiation diameter=250 nm) to thealuminum nanoparticles having a longer diameter of about 15 nm togetherwith the amorphous carbon thereunder.

While irradiating the electron beam, a states of the aluminumnanoparticles and the amorphous carbon in TEM was observed in-situ. Withreference to schematic diagrams of FIG. 1A and FIG. 1B, the observedresult will be described. After 300 seconds irradiation of the electronbeam, carbon structure 2 having an elliptic and concentric circle with alonger diameter of 15 nm under the aluminum nanoparticle 1 was produced,as shown in FIG. 1A. Because a distance between layers of the carbonstructure having an elliptic and concentric circle was about 0.35 nm,the carbon structure was identified as an onion-like graphite 2. Aroundthe onion-like graphite 2, the amorphous carbon 3 still existed.

While further irradiating the electron beam, the onion-like graphite 2shrank gradually to become smaller in a concentric circle shape, and thealuminum nanoparticle 1 also became smaller. After 800 to 1000 secondsirradiation of the electron beam, the onion-like graphite 2 shrank inthe concentric circle shape, and the aluminum nanoparticle 1 becamesmaller to have a diameter of 2 nm, as shown in FIG. 1B. FIG. 2 shows achange of longer (Al-a) and shorter (Al-b) diameter of the aluminumnanoparticle 1 and a change of longer (G-a) and shorter (G-b) diameterof the onion-like graphite 2 with the elapsed time of the irradiation ofthe electron beam. As apparent-from FIG. 2, the aluminum nanoparticle 1and the onion-like graphite 2 in elliptic shapes shrank to becomecircular shapes.

With becoming smaller, aluminum atoms (atom aggregates) constituting thealuminum nanoparticle 1 were intercalated in a space (van der Waals bondlayer) between (001) plane and (002) plane of the onion-like graphite 2having a layer structure to form a graphite intercalation compound 4.The graphite intercalation compound 4 was identified with EnergyDispersive X-ray Spectoroscopy (EDS). A distance between layers of theonion-like graphite 2 widened to 0.40 nm in spite of 0.334 nm in normalstatus. Twenty percent of lattice distortion existed.

In the graphite intercalation compound 4, the aluminum atom aggregatesconstituting the aluminum nanoparticle 1 were arranged so as to parallel{002} plane of the aluminum nanoparticle 1 with the (002) plane of theonion-like graphite 2. The aluminum aggregates and the onion-likegraphite 2 were in epitaxy relations. Lattice spacing d between the(001) plane and the (002) plane of the onion-like graphite 2 where thealuminum atoms were clearly identified was 0.40 nm. Lattice of theonion-like graphite 2 expanded to be twice the length of 0.20 nm (whichis a distance between the (200) planes of the aluminum). In thisportion, crystal structure may be equivalent to that of Al₂ C₆.

FIG. 3 shows a change of a lattice spacing d of each portion (A, B, C)of the onion-like graphite 2 with the elapsed time of the irradiation ofthe electron beam. As apparent from FIG. 3, aluminum atoms dispersed ineach portion of the onion-like graphite 2.

Thus, by irradiating the electron beam to the onion-like graphite 2 uponwhich the aluminum nanoparticle 1 was disposed, the graphiteintercalation compound 4 that aluminum atoms (aluminum atom aggregates)constituting the aluminum nanoparticle 1 were intercalated into thespace between the (001) plane and the (002) plane of the onion-likegraphite 2 having a layer structure was obtained. This production of thegraphite intercalation compound 4 is apparently based on both alocalized heating effect and an atom displacement (knock-on) effect bythe irradiated electron.

Embodiment 2

Production of an onion-like graphite and aluminum nanoparticles will bedescribed. First, spherical θ-Al₂ O₃ particles (purity 99.8%) with adiameter of about 100 nm were prepared. The particles were dispersed inalcohol, applied to an amorphous carbon support film made of i-carbonand dried. Secondly, the amorphous carbon support film disposedspherical θ-Al₂ O₃ particles were arranged in a room temperature stagewhich was disposed in a vacuum chamber of 200 kV TEM (JEOL, JEM-2010).

Thirdly, the vacuum chamber was evacuated to 1×10⁻⁵ Pa. Fourthly, anelectron beam having an intensity of 1.3×10²⁰ e/cm² ·sec (20A/cm²) wasirradiated to the θ-Al₂ O₃ particles having a diameter of about 100 nmdisposed on the amorphous carbon support film. With the irradiation ofthe electron beam, an onion-like graphite having a diameter of about 10to 30 nm and aluminum nanoparticles having a diameter of about 5 to 10nm were produced on the amorphous carbon support film.

FIG. 4 shows an observed result of a states of the onion-like graphiteand the aluminum nanoparticles in TEM. As shown in FIG. 4, byirradiating the electron beam to the θ-Al₂ O₃ particles, α-Al₂ O₃particles 5 which was smaller than the θ-Al₂ O₃ was produced. Around theα-Al₂ O₃ particle 5, an aluminum nanoparticle 6 having a diameter ofabout 5 to 10 nm and an onion-like graphite 7 having a diameter of about10 to 30 nm were produced. Around the initial θ-Al₂ O₃ particles, acarbon nanocapsule 8 having a diameter of about 20 nm and a carbonnanotube 9 having a thickness of about 10 nm were also produced.

Using the onion-like graphite and the aluminum nanoparticles, a graphiteintercalation compound was produced. A status of the production in TEMwas observed in-situ. With reference to schematic diagrams of FIG. 5Aand FIG. 5B, the observed result will be described. The onion-likegraphite 7 having a longer diameter of about 15 nm and the aluminumnanoparticle 6 having a diameter of about 5 nm near the graphite wereselected. With irradiating and scanning the electron beam to thealuminum nanoparticle 6, the aluminum nanoparticle 6 was driven anddisposed on the onion-like graphite 7, as shown in FIG. 5A.

An electron beam having an intensity of 1.3×10²⁰ e/cm² ·sec (20A/cm²)was irradiated (irradiation diameter=250 nm) to the onion-like graphite7 driven and disposed the aluminum nanoparticle 6. After the elapsedtime of the irradiation, the onion-like graphite 7 shrank gradually tobecome smaller. After 560 seconds irradiation of the electron beam, agraphite intercalation compound 10 that aluminum atoms (aluminum atomaggregates) constituting the aluminum nanoparticle 6 were intercalatedinto a space (between van der Waals bonding layers) between (001) planeand (002) plane of the onion-like graphite 7 having a layer structurewas obtained, as shown in FIG. 5B. In the graphite intercalationcompound 10, the onion-like graphite 7 had a longer diameter of about 10nm and the aluminum nanoparticle 6 had a diameter of about 2 nm.

Thus, by irradiating the electron beam to the onion-like graphite uponwhich the aluminum nanoparticles were driven and disposed, a graphiteintercalation compound intercalated the aluminum nanoparticles into thespace between the (001) plane and the (002) plane of the onion-likegraphite having a layer structure was obtained. This production of thegraphite intercalation compound is apparently based on both a localizedheating effect and an atom displacement (knock-on) effect by theirradiated electron.

As apparent from these embodiments, according to the present invention,the intercalation compound can be produced by irradiating the electronbeam and intercalating the aluminum atoms in the space between the (001)plane and the (002) plane of the graphite having a layer structure undereasily controllable conditions of room temperature stage. Therefore,various manipulations with electron beams having a diameter in-nanometercan-be realized.

As described above, according to the present invention, for example, thegraphite intercalation compound can be produced on a specified nanoscalearea of the graphite, therefore controllability of states, shape and/ordistribution of the graphite intercalation compound are remarkablyenhanced. With satisfying such requirements, the intercalation compoundthat the aluminum atoms are intercalated in the space of the graphitehaving a layer structure can be obtained repeatedly.

What is claimed is:
 1. A method for producing a graphite intercalated compound comprising the steps of:disposing an active aluminum nanoparticle on graphite having a multi-layer concentric spherical structure, said multi-layer concentric spherical structure including crystal faces corresponding to a (001) plane and a (002) plane of the graphite, and irradiating an electron beam on said graphite with the aluminum nanoparticle under a vacuum atmosphere to shrink said graphite and simultaneously intercalate aluminum atoms constituting the aluminum nanoparticle in a space between said crystal faces of said graphite.
 2. A method as claimed in claim 1, wherein said graphite is produced by disposing a metastable aluminum oxide particle on amorphous carbon, and by irradiating the electron beam on the metastable aluminum oxide particle under a vacuum atmosphere.
 3. A method as claimed in claim 1, wherein the electron beam has an intensity of 1×10¹⁹ e/cm² ·sec or more.
 4. A method as claimed in claim 1, wherein said graphite is produced by disposing an active aluminum nanoparticle on amorphous carbon, and by irradiating the electron beam on the amorphous carbon with the aluminum nanoparticle under a vacuum atmosphere. 